The present invention generally relates to fabrication of semiconductor devices and more particularly to a dicing of a semiconductor wafer into individual semiconductor chips while covering the semiconductor wafer by a tape.
In the fabrication process of semiconductor devices, a number of semiconductor devices are formed on a common semiconductor wafer. The wafer thus formed with the semiconductor devices are then subjected to a dicing process in which the semiconductor wafer is divided into individual chips by a saw.
In this dicing process, a tape or other suitable adhesive medium is provided on a rear side of the semiconductor wafer, opposite to the side on which the semiconductor devices are formed, and the dicing is carried out in such a state so that the chips formed as a result of the dicing do not scatter. Thereby, only the semiconductor wafer is diced, while the tape itself remains intact. By using such a tape, the semiconductor chips maintain the arrangement on the tape even after the dicing process, and the use of automatic assembling apparatus that picks up the chips one by one is substantially facilitated.
However, a typical semiconductor wafer, typically having a thickness of 320 .mu.m, tends to warp such that a front side where the semiconductor devices are formed is projected and the opposite, rear side is concaved. Thus, mere attachment of a tape on the rear side of the wafer tends to leave a void at the central part of the concaved rear surface, and the semiconductor chips corresponding to such a central part of the wafer tend to litter or scatter after the dicing process because of the poor adherence to the tape.
In order to prevent such a scattering of the chips as well as possible damages to the chips thus scattered, a conventional apparatus used for attaching the tape applies a roller on the taped surface of the substrate as indicated in FIG. 1.
Referring to FIG. 1, a semiconductor wafer 1 held on a stage 2 of the tape attachment apparatus is covered by an adhesive tape 4 on the upper principal surface thereof, wherein the tape 4 is held on a frame 3. No semiconductor devices are formed on the upper principal surface of the substrate. Further, a roller 5 is urged against the tape 4 from an upward direction and is moved over the tape 4 such that any void between the tape 4 and the upper major surface of the substrate 1 is collapsed. It should be noted that the attachment of the tape 4 is carried out in a vacuum environment. Thus, the apparatus of FIG. 1 is placed in a vacuum chamber.
However, the apparatus of FIG. 1 has a drawback in that it is necessary to provide a mechanism that urges the roller 5 against the tape 4 and move the roller 5 over the tape 4. Thereby, it is necessary to provide a very large vacuum chamber for accommodating the apparatus of FIG. 1, while use of such a large volume vacuum chamber necessitates a substantial time for evacuation. Further, use of such a roller 5, which urges one point at a time, may cause a damage to the wafer 1 due to an excessive load. Further, use of such a roller 5 tends to cause a deformation of the adhesive tape 4 on the upper major surface of the substrate 1 as a result of the pressure applied to the tape 4 by the roller 5. When the tape 4 is deformed, the semiconductor chips obtained after the dicing may be displaced from the nominal position and the use of automatic assembling apparatus for picking up the chips becomes difficult.
FIG. 2 shows another conventional construction for attaching a tape on a semiconductor wafer before dicing, wherein those parts corresponding to the parts described heretofore are eliminated.
Referring to FIG. 2 showing a wafer stage 8 provided in a lower chamber 7 and an upper chamber 6 provided on the lower chamber 7 to form a vacuum chamber, it should be noted that the lower chamber 7 is evacuated to a pressure P.sub.2 while introducing the air to the upper chamber 6 via a duct 9 such that the pressure inside the upper chamber 6 becomes P.sub.1. The pressure P.sub.1 is thus higher than the pressure P.sub.2 (P.sub.1 &gt;P.sub.2).
As a result of such a pressurization of the upper chamber 6, the tape 4 is bulged in the direction of the lower chamber 7, forming a projecting surface on the side facing the semiconductor wafer 1 as indicated in FIG. 2. By lifting up the wafer stage 8 and hence the wafer 1 in the upward direction in this state, the tape 4 first contacts with the center of the concaved surface of the waver 1. With further upward movement of the stage 8, the area of contact increases gradually from the center to the rim of the wafer 1, without forming a void between the wafer 1 and the tape 4.
In the construction of FIG. 2, it is necessary to control the pressures P.sub.1 and P.sub.2 such that the pressure actually acting upon the tape 4 is held constant and optimum. However, such an adjustment of the pressure P.sub.1 in the upper chamber 6 and the pressure P.sub.2 in the lower chamber 7 is difficult. When the pressure P.sub.1 is too low, for example, sufficient urging force is not obtained for applying the tape 4 against the wafer 1. When the pressure P.sub.1 is too high, on the other hand, the bulging of the tape 4 as well as the tensile force acting on the tape 4 becomes excessive, and the tape 4 experiences a plastic deformation. Thereby, the semiconductor chips on the tape are, after the dicing process, displaced from the nominal position, and the use of the automatic assembling apparatus becomes difficult.
FIG. 3 shows a further conventional apparatus for applying a tape upon a concaved surface of a semiconductor wafer as disclosed in the Japanese Laid-open Patent Publication 4-65109, wherein those parts described previously are designated by the same reference numerals and the description thereof will be omitted.
Referring to FIG. 3, there is provided a movable member 9 movable in up and down directions in the upper chamber 6, wherein the movable member 9 carries thereon a deformable, resilient member 10 that has a shape protruding or bulging in the downward direction in correspondence to the concaved upper major surface of the wafer 12. By lowering the movable member 9, the bulging surface of the resilient member 10 engages with the tape 4 and causes the tape to bulge in the downward direction. Thus, by lifting the stage 8 in the upward direction in the state that the tape 4 is bulged in the downward direction, the tape 4 first engages with the center of the concaved surface of the wafer 1, and the area of the contact increases gradually toward the rim of the wafer 1 with further lifting-up of the stage 8.
However, the apparatus of FIG. 3, relying upon the mechanical deformation of the resilient member 10 for causing the desired deforming the tape 4, also has a problem in that the control of the urging force of the tape 4, particularly the distribution of the urging force over the concaved surface of the wafer 1, is difficult. In view of the very small thickness of the wafer 1, such a construction, in which the urging force of the tape 4 acting over the wafer 1 is controlled by the respective urging forces of the movable members 8 and 9 and further by the resiliency of the deformable member 10, there is a substantial risk that the wafer 1 is damaged during the process of applying the tape 4 thereon.